From 8b50e6b67c77cfe254fa8d59e9018dc69603fc7a Mon Sep 17 00:00:00 2001
From: P. J. McDermott <pjm@nac.net>
Date: Sat, 02 Mar 2013 15:30:29 -0500
Subject: src/main.c: Use cosine curve for day-night cycle.

---
diff --git a/src/main.c b/src/main.c
index d2f10f9..842a20c 100644
--- a/src/main.c
+++ b/src/main.c
@@ -1,3 +1,4 @@
+#include <math.h>
 #include <SDL.h>
 #include "init.h"
 #include "logging.h"
@@ -61,14 +62,29 @@ main(void)
 	render_area_to_viewport(a, vp);
 	{
 		float step;
-		for (step = 1.0; step >= 0.25; step -= 0.00390625) {
+		int y_start, y_end;
+		for (step = 0.0; step < 12.57; step += 0.006136) {
 			for (i = 0; i < 256; ++i) {
-				colors[i].r = (i % 8) * 36;
-				colors[i].g = (i % 64 / 8) * 36;
-				colors[i].b = (i / 64) * 85;
-				colors[i].r *= step;
-				colors[i].g *= step;
-				colors[i].b *= step;
+				/*
+				 * ((cos(x) + 1) / 2) => [0,1]
+				 * y = ((cos(x) + 1) / 2) *
+				 *     (y_end - y_start) + y_start
+				 */
+
+				y_start = (i % 8) * 36;
+				y_end = y_start / 4;
+				colors[i].r = ((cos(step) + 1) / 2) *
+					(y_end - y_start) + y_start;
+
+				y_start = (i % 64 / 8) * 36;
+				y_end = y_start / 4;
+				colors[i].g = ((cos(step) + 1) / 2) *
+					(y_end - y_start) + y_start;
+
+				y_start = (i / 64) * 85;
+				y_end = y_start / 4;
+				colors[i].b = ((cos(step) + 1) / 2) *
+					(y_end - y_start) + y_start;
 			}
 			if (!SDL_SetPalette(vp->screen, SDL_LOGPAL, colors, 0, 256)) {
 				warn("Failed to set palette");
--
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